This proposal describes assessment of the clinical utility of a quantitative molecular assay using patented monoclonal antibodies, fluorescence, analytical software, and flow cytometry technology for a white blood cell molecule, called CD64. The expression of CD64 increases rapidly on the blood leukocyte neutrophil subpopulation due to molecular activation of these cells by inflammatory mediators or cytokines. Quantitative measurement of neutrophil CD64 expression with this assay, named Leuko64, can identify the systemic acute inflammatory response occurring in patients with sepsis, infection or tissue injury. The Leuko64 assay is anticipated to have medical utility in the triage of patients with suspected infection to appropriate medical therapy, assist in therapeutic monitoring of patients on antibiotic therapy and thereby reduce the unnecessary use of antibiotics, thus minimizing the pressure for the development of antibiotic resistant organisms. The Leuko64 assay represents one of the first diagnostic assay systems to utilize cellular molecular changes to detect and monitor the immune response to infection and sepsis. The objectives of this proposal are to 1) validate the clinical performance of Leuko64, 2) demonstrate its superiority as a diagnostic assay for detection of infection and sepsis compared to the clinical laboratory tests currently used in contemporary medical practice, 3) confirm the reliability of the automated proprietary computer software developed during the phase I work, 4) develop a stabilized assay control product for the assay, and 5) to develop a prototype second generation assay integrated into a hematology blood cell counter.